As the climate warms and some tree species shift toward cooler, more hospitable habitats, new research finds soil microbes could be playing a crucial role in determining where young trees can migrate and how well they survive when they arrive.

Much like humans, whose guts and skin are teeming with microbes, the soil below plants and trees contains a unique cornucopia of microscopic creatures that help the tree take in nutrients and water.

Published in the journal Nature Ecology & Evolution, a new study finds nuance in the role played by soil biota. In some instances, the tiny fungi and bacteria constrain where offspring can grow, but in higher elevations — where the species is headed as the climate warms — a less robust soil microbiome seems to create conditions where baby trees can thrive upslope.

Jennifer Schweitzer, an associate professor at the University of Tennessee, Knoxville, and co-author of the paper, said forest managers and conservationists may consider accounting for a tree's microscopic soil creatures in the future, as they could determine how quickly species march toward cooler conditions.

“We tend to think that the factors that determine where forests are on a landscape are largely driven by climate, but what these data show is soils and the soil microbiome community might be a lot more important than we have appreciated in the past,” she said.

The researchers analyzed the differences in the soil microbiome based on the location of a common species of poplar tree. Populus angustifolia, more commonly known as a cottonwood, is widely found across North America, from arid Arizona to the Canadian Rocky Mountains, and from mid-elevation habitats to peaks more than 8,000 feet high.

The researchers, all hailing from the University of Tennessee, Knoxville's Department of Ecology and Evolutionary Biology, trekked into the Rocky Mountains to collect soils and seedlings beneath cottonwood trees at low and high elevations.

They found that the soil microbiomes below the trees looked very different depending on where the cottonwood in question was located.

Back in the lab, the team simulated the species' shift upslope by transplanting baby trees from lower elevations into soils collected up in the mountains.

It found that for trees in the comfortable middle of their range, down near the base of a mountain, their offspring thrived nearby in the rich, microbe-filled soil collected right below their parent.

But for trees farther up in elevation, the researchers found the offspring did better when they moved even farther up the mountain.

“That creates conditions where offspring continue to move up the mountain and populations are going to split,” Schweitzer said.

If the cottonwood species becomes fragmented and the climate continues to warm, lower-elevation cottonwoods may find themselves stranded, she said.

Schweitzer said planting cottonwoods in higher elevations with soil from favorable areas could help the trees succeed and keep forests intact as the climate changes.

“Trees vary even within a species, and their microbes vary, and their microbes might help or hinder when the species responds to climate change,” she said. “These positive and negative interactions with microbes might really change population fragmentation patterns.”

Wim van der Putten, head of the Department of Terrestrial Ecology at the Netherlands Institute of Ecology, praised the researchers for their work and said it was the first time he had seen seen an experiment in which transplants were used to test how a species would react when moved to a different area typically colonized by a genetically different part of the species' population.

“Microbes are a very diverse group of organisms. There are good kinds, bad kinds, and the interplay between the good and bad kinds determines if the species ultimately benefits or suffers from range shift,” said van der Putten, who was not associated with the study. “If you move outside of the range of your enemies you could benefit, but if you move away from symbionts and decomposers, that could make it harder for them to get established.”

Scientific understanding of how specific groups of bacteria interact with plant species is still in its infancy, noted Samantha Chapman, an associate professor in the Department of Biology at Villanova University.

She said the study highlighted how soil bacteria can mediate range shifts upslope for species, a factor that is especially important in a warming climate.

“The novelty of their findings are they are looking into areas where plants aren't yet, but might get to,” Chapman said.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.

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